1. Technical Field
The present disclosure relates generally to intervertebral implants for spinal fusion and, more particularly, to a ramp-shaped intervertebral implant having a top surface and a bottom surface and at least one opening extending between the top and bottom surfaces.
2. Background of Related Art
Surgical procedures for fusing adjacent vertebrae together to treat back pain in patients with ruptured or degenerated intervertebral discs, spondylolisthesis or other pathologies are well known. Typically during such a procedure, a spinal implant is placed into the intervertebral space in a position to engage adjoining vertebrae. The implant is constructed from a biocompatible material which is adapted to fuse with the adjacent vertebrae to maintain proper spacing and lordosis between the adjacent vertebrae, i.e., maintain the disc space.
A variety of different types of intervertebral implants have been developed to perform this function including spinal fusion cages, threaded bone dowels and stepped bone dowels. Exemplary implants are disclosed in U.S. Patent Applications filed on even date herewith, under Certificate of Express Mail Label Nos. EL260888080US and EL071686220US, and entitled "Intervertebral Implant" and "Keyed Intervertebral Dowel", respectively, the entire disclosures of which are incorporated herein by reference.
One type of intervertebral implant has a wedge configuration. U.S. Pat. No. 5,425,772 to Brantigan discloses a wedge-shaped implant having an anterior end, a posterior end, front and rear walls, top and bottom walls and sidewalls. The implant is constructed from biocompatible carbon reinforced polymer or alternately of traditional orthopedic implant materials such as chrome cobalt, stainless steel or titanium. The top and bottom walls are tapered from the anterior end of the implant to the posterior end such that the anterior end of the implant has a height greater than the height of the posterior end of the implant. The top and bottom of the implant are continuous and unslotted and include a series of transverse teeth or serrations extending thereacross. A slot configured to receive bone graft material extends through the implant between the sidewalls.
During insertion of Brantigan's implant into the intervertebral space, the adjoining vertebrae are tensioned and a portion of disc tissue between the vertebrae is cut and removed to form channels between the vertebrae. The implant is positioned in the channel such that the teeth formed on the top and bottom surfaces of the implant engage the adjoining vertebrae. During a surgical spinal fusion procedure, two of Brantigan's implants are inserted between the adjoining vertebrae to be fused.
U.S. Pat. No. 5,443,514 to Steffee also discloses a wedge-shaped implant having upper and lower toothed surfaces, a pair of parallel side surfaces, a pair of end surfaces and a plurality of openings extending between the side surfaces. The implant is constructed from an injection molded chopped carbon fiber reinforced polymer. The openings facilitate blood flow and bone growth from one side of the implant to the other. Steffee's implant is adapted to receive an insertion tool which during insertion of the implant between adjoining vertebrae rotates the implant from a horizontal to a vertical orientation. During a surgical procedure, two of Steffee's implants are positioned between adjoining vertebrae.
Conventional wedge-shaped intervertebral implants, including those described above, have several drawbacks. For example, although autograft wedges are known, e.g., iliac crest wedges, typically, conventional wedge-shaped implants are constructed from materials which do not remodel but rather remain in place forever or until removal is necessitated, i.e., at least some or all of the implant is not replaced by new bone, but rather the implant itself is incorporated into the body. Since the implants usually become adherent to the adjoining vertebrae, if removal of the implant is ever necessitated, the procedure to effect removal is complicated and dangerous to the patient. Moreover, in conventional wedge-shaped implants, the opening(s) to facilitate bone ingrowth extend transversely through the implant and as such do not open in communication with the adjoining vertebrae. Thus, bone ingrowth and eventual fusion will occur more slowly.
Accordingly, a need exists for an improved wedge-shaped intervertebral implant which can be easily manufactured from a material which will be remodeled within the body and will more quickly become adherent to adjoining vertebrae.